1. Field of the Invention
The present invention relates to a stack arrangement having at least two workpieces, a first workpiece and at least one another workpiece, and connected by an eyelet, with the material of the first workpiece being drawn through a through-opening in the at least one another workpiece. The present invention also relates to a method of forming the eyelet that includes forming, with a piercing die, through-openings in the first workpiece and the at least one another workpiece, with the through-opening in the first workpiece having a cross-section smaller than the cross-section of the eyelet and with the through-opening in the at least one another workpiece having a cross-section greater than the cross-section of the eyelet and drawing, with a plunging die displaceable through the stack perpendicular thereto, material of the first workpiece through the through-opening in the at least one another workpiece.
2. Description of the Prior Art
German Utility Model DE 8632788 U1 discloses a stack of arranged one above another pre-formed flat parts connected with each other by an eyelet. The flat parts, before being riveted with each other, are separately provided, in a separate operational step, with openings. Upon arrangement of the parts at the site one upon another, the openings are arranged congruently with each other, with the opening in the outwardly located flat part adjacent to the plunging die being smaller than openings in the remaining parts. With the plunging die, the material of the flat part adjacent to the plunging die is drawn through the openings of other parts remote from the plunging die, with free rim of the eyelet being finally bent outwardly.
The drawback of the arrangement of DE 86 32788 U1 consists in that the flat parts should be provided separately with openings in precisely predetermined locations. Further, it should be preliminarily decided which flat part would be used for forming the eyelet. The disclosed method is rather complicated and error-prone.
German Patent DE 198 10 367 C1 discloses a method of forming an eyelet extendable through a stack of at least two plate-shaped workpieces, and according to which, a through-opening is formed in the stack before forming the eyelet, with the cross-section of the through-opening at most corresponding to the cross-section of the eyelet. Finally, a plunging die is displaced through the stack substantially perpendicular thereto, with the material of the workpiece adjacent to the plunging die being drawn through the through-opening of the workpiece remote from the plunging die. The inner profile of the opening substantially corresponds to the outer profile of the eyelet. With a single movement of the plunging die, both the eyelet and the opening in the workpiece remote from the plunging die, are formed. The workpiece remote from the die is so supported by a stamp that upon displacement of the plunging die out of the workpiece remote therefrom, a piece of material breaks off the remote workpiece. The outer profile of the material piece substantially corresponds to the outer profile of the eyelet. The free rim of the eyelet is flanged out outwardly.
The disclosed method of forming a riveting eyelet has proved itself. However, at a thickness of material above 3 mm, it hits against its limits. In addition, tension and transverse loads, which are produced according to this method, cannot be increased further.
An object of the present invention is a stack arrangement formed of at least two plate-shaped workpieces connectable with each other by an eyelet produced with a plunging die, and a method of forming the eyelet that enables connection of the workpieces independent of the thickness of material and transmission of large loads by the produced rivet joint.